1. Field of the Invention
The present invention relates to a process for producing fiber aggregate, and more particularly, it relates to a process for producing fiber aggregate in which most fibers are about one-dimensionally oriented, by utilizing an AC power source. "One-dimensionally oriented" means that many fibers are oriented in substantially the same direction. This definition is applied not only to the fiber aggregate but also to the orientation step mentioned later.
2. Prior Art
Heretofore, fiber aggregate of short fibers or whiskers has been produced in the following means.
A centrifugal forming method which employs a centrifugal forming apparatus as shown in FIG. 3 (Japanese Unexamined Patent Publication No. 65200/1985). According to this method, an aqueous suspension of silicon carbide whiskers or the like is fed through the supply pipe 24 to the porous long cylindrical vessel 23 which is lined with the filtration film 25 and disposed in the outer cylinder 21. The cylindrical vessel 23 is rotated rapidly. As a result, fibers are attracted toward the inner surface of the cylindrical vessel 23. Then water is discharged from the outlet 22 and cylindrical fiber aggregate 26 is formed on the inner surface of the cylindrical vessel 23.
Another conventional method which employs a suction forming apparatus is as shown in FIG. 4. According to this method, a prescribed amount of fiber-containing fluid 34 is fed to the cylinder 31, and a pressure is applied to the fluid 34 by the plunger 32 arranged above the cylinder 31. At the same time, the filtrate is removed by vacuum suction through the filter 33 disposed at the bottom of the cylinder 31. Thus the fibers in the fluid are oriented and aggregate.
Other conventional methods include the papermaking method and spraying method.
The fiber aggregate formed by the centrifugal method or suction method is not composed of one-dimensionally oriented fibers, but is composed mainly of two dimensionally oriented fibers. The fiber aggregate with such orientation has a disadvantage that it does not provide a sufficient strength in the desired one-dimensional direction when incorporated into fiber-reinforced metal (referred to as FRM hereinafter). Additional disadvantages are the low volume ratio of fiber. If fibers are two- or three-dimensionally oriented, there is apt to be produced some space between fibers. Consequently, a density of fibers in a given space becomes lower accordingly.